The effects of prostaglandin E on fetal pulmonary vascular resistance (38588)

Persistent pulmonary hypertension of the newborn: recent advances in pathophysiology and treatment

OBJECTIVES

Although recognized for decades, little is known about the etiology, physiopathology, and prevention of persistent pulmonary hypertension of the newborn (PPHN), and its treatment remains a major challenge for neonatologists. In this review, the clinical features and physiopathology of the syndrome will be addressed, as well as its general and specific treatments.

DATA SOURCE

A review was carried out in PubMed, Cochrane Library, and MRei consult databases, searching for articles related to the syndrome and published between 1995 and 2011.

DATA SYNTHESIS

Risk factors and the physiopathological mechanisms of the syndrome are discussed. The clinical presentation depends on the different factors involved. These are related to the etiology and physiopathology of the different forms of the disease. In addition to the measures used to allow for the decrease in pulmonary vascular resistance after birth, in some instances pulmonary vasodilators will be required. Although inhaled nitric oxide has proved effective, other vasodilators have been recently used, but clinical evidence is still lacking to demonstrate their benefits in the treatment of PPHN.

CONCLUSIONS

Despite recent technological advances and new physiopathological knowledge of this disease, mortality associated with PPHN remains at 10%. More clinical research and evidence-based experimental results are needed to prevent, treat, and reduce the morbidity/mortality associated with this neonatal syndrome.

The role of lung perfusate PO2 in the control of the pulmonary vascular resistance of exteriorized fetal lambs

The isolated perfused lower left lung lobe of the exteriorized fetal lamb was used to define quantitatively the relationship between pulmonary perfusate oxygen tension and pulmonary vascular resistance (PVR) in the fetus at multiple oxygen tensions over the range from 8.3 to 433 mm Hg. This allowed variation of the perfusate PO2 over the range of partial pressures from less than 10 mm Hg to over 400 mm Hg while constant values of PCO2, temperature and perfusate flow were maintained. In all animals, calculated pulmonary vascular resistance varied in an inverse manner with the perfusate PO2. The relationship between PVR and perfusate oxygen tension is described by the equation: PVR = 7.67 - 1.54 (log PO2) R2 = 0.70. While others have shown that a single, large increase in blood oxygen tension will decrease the PVR in fetal lambs, these data present the first quantitative description of the role of oxygen tension in the modulation of fetal pulmonary vascular resistance as determined at multiple perfusate oxygen tensions over a fifty-fold range.

Effect of prostaglandin E1 on pulmonary circulation in pulmonary atresia. A quantitative morphometric study

The structural effect of prostaglandin E1 on the pulmonary circulation in pulmonary atresia has been studied by applying quantitative morphometric techniques to the injected and inflated lungs of eight babies who had received prostaglandin E1 for between 30 hours and 12 days. The most striking effect was on the pulmonary arterial smooth muscle. Relative arterial medial thickness was reduced and muscle did not extend as far along the arterial pathway as compared with the normal and with untreated cases of pulmonary atresia, dying at a similar age. The reduction in muscularity tended to increase the longer the duration of infusion. In all cases the thin arterial media was less compact than normal, and localised aneurysmal dilatations occurred, varying in extent and severity between cases. The preacinar arteries were dilated in comparison with the untreated cases, but, by contrast, the intra-acinar arteries remained abnormally small. The number of intra-acinar arteries per unit area of lung was greater in prostaglandin E1 treated than in untreated cases. Infusion of prostaglandin E1 is now the ideal emergency treatment for pulmonary atresia, but the findings in the present study suggest that it should be given for as short a time as possible before the pulmonary blood flow is increased by surgical treatment.

Hemodynamic, pulmonary vascular, and myocardial abnormalities secondary to pharmacologic constriction of the fetal ductus arteriosus. A possible mechanism for persistent pulmonary hypertension and transient tricuspid insufficiency in the newborn infant

The prostaglandin synthetase inhibitor indomethacin was given orally or intravenously to pregnant ewes. This resulted in a significant rise in the fetal pulmonary-to-systemic arterial mean blood pressure difference across the ductus arteriosus, presumably secondary to constriction of the ductus arteriosus. In five experiments the pressure difference could be promptly but temporarily reversed by the administration of prostaglandin E1 (PGE1) into the fetal inferior vena cava. Fetal lungs from study and control animals were fixed by perfusion at measured pulmonary arterial mean blood pressure, and fifth-generation resistance vessels were studied. The medial width/external diameter ratio was significantly increased in the study vs the control lungs due to increased smooth muscle and decreased external diameter. In addition, study fetuses had acute degenerative myocardial changes in the tricuspid valve papillary muscles, the right ventricular free wall and the interventricular septum. Similar changes were not seen in control fetuses. Indomethacin administration during pregnancy causes constriction of the fetal ductus arteriosus, fetal pulmonary arterial hypertension, and right ventricular damage. If severe, this may cause rapid fetal death. If less severe, in the newborn infant, this mechanism may be one cause of persistent pulmonary hypertension due to vasoconstriction and increased pulmonary arterial smooth muscle and/or tricuspid insufficiency due to papillary muscle infarction.

Premature labor and indomethacin

Administration of indomethacin to 29 women in the 26th--37th week of gestation with premature labor contractions was followed in 26 by a significant decrease of uterine activity. The effect of therapy was monitored by serial external tocometry recordings and by plasma concentrations of estriol, h.P.L., alpha-fetoprotein, and estriol/creatinine ratio in urine. The labor was monitored by cardiotocography; the new born infants were examined by the pediatrician. Following oral indomethacin treatment (25 mg every 6 Hours for 5 days) no untoward effects was observed on maternal and fetal wellbeing during pregnancy and labor. Four out 29 newborn infants, all appropriate for gestational age of 36--40 weeks, had one-minute Apgar scores less than 7, cyanosis, tachypnea, hypoxemia and serious oxygen dependency for several days. All the infant survived. These abnormalities may be due to short-term exposure to indomethacin and consequent inhibition of cyclo-oxygenase, impairement of prostaglandin-dependent physiological regulation of vessel tone during fetal life and circulatory disorders at birth.

Administration of prostaglandin E1 in neonates with critical congenital cardiac defects

Prostaglandin E1 was administered to 12 neonates and young infants in whom pulmonary or systemic blood flow was entirely or significantly dependent upon persistent patency of the ductus arteriosus. Nine neonates responded favorably to PGE1 infusion; their mean age was 2.8 days. Three infants who failed to respond were 10 days, 14 days, and 9 weeks of age, respectively. Six neonates with right ventricular outflow obstruction had a mean increase in arterial PO2 of 136% following administration of PGE1. In three patients in whom systemic flow was ductus dependent, PGE1 infusion was followed by improvement in arterial blood pressure, peripheral perfusion, and urine output. Complications included pyrexia, vasodilatation, and myoclonic jerks (or focal seizures). Three side effects were easily reversible by decreasing the infusion rate or altering the site of administration. PGE1 is a highly effective agent in stabilizing critically ill neonates with ductus dependent congenital cardiac lesions.

Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors

Since the effects of prostaglandin synthetase inhibitors on the developing human fetal pulmonary vasculature are unknown, we studied the lungs of two infants, one whose mother took salicylates and the other whose mother took indomethacin during pregnancy. Lungs were fixed by perfusion and fifth generation (resistance) vessels identified. The infant with chronic exposure to aspirin had premature constriction of the ductus arteriosus, tricuspid insufficiency, increased pulmonary arterial medial width/external diameter ratio due to increased smooth muscle, and a decreased number of pulmonary vessels/cm2 lung tissue. The infant with short-term exposure to indomethacin had hypoxemia, increased pulmonary arterial m/d ratio due to increased smooth muscle, and a normal number of pulmonary vessels/cm2 lung tissue. These abnormalities may be due to the effects of prostaglandin synthetase inhibitor drugs on the ductus arteriosus and/or the pulmonary vessels of the human fetus.

Use of prostaglandin E1 for emergency palliation of symptomatic coarctation of the Aorta

Prostaglandin E1 (PGE1) was infused into the pulmonary artery in a 1-day-old infant with symptomatic coarctation. Umbilical artery pressure rose from 50/40 mm Hg before infusion to 83/48 mm Hg after infusion, indicating significant improvement in lower-body perfusion. Successful coarctation repair was performed during continued PGE1 infusion. To our knowledge, this is the first reported patient in whom PGE1 has been used for successful emergency palliation of symptomatic coarctation.

Effects of acetylsalicylic acid on the ductus arteriosus and circulation in fetal lambs in utero

Intra-arterial and intravenous catheters were inserted in six fetal lambs at 125-130 days of gestation. On the following day, fetal arterial pressures and blood gases were monitored and fetal cardiac output and its distribution were measured by injection of radionuclide-labeled microspheres 15 mum in diameter. Acetylsalicylic acid, 55-90 mg/kg of estimated fetal weight, then was administered into the fetal stomach. Fetal pulmonary arterial pressure rose significantly after an average of 58 minutes, increasing the pressure difference between the pulmonary artery and the aorta from 2 +/- 0.3 (SEM) mm Hg during control to 11.2 +/- 1.6 mm Hg. Resistance across the ductus arteriosus rose from 4.2 +/- 0.5 (SEM) to 27.4 +/- 4.01 units, and flow fell from 495 +/- 44 (SEM) to 409 +/- 20 ml/minute. The proportion of combined ventricular output distributed to the placenta, adrenals, heart, and lungs increased, whereas the proportion of combined ventricular output distributed to the brain, liver, intestine, kidneys, and upper and lower body fell. In two fetuses infusion of prostaglandin E1 reversed the pulmonary hypertension. Inhibition of prostaglandin synthesis in fetal lambs produced constriction of the ductus arteriosus and redistribution of cardiac output. It is probable that prostaglandins, particularly E1, are involved in regulation of blood flow through the ductus arteriosus and various vascular beds in the normal resting fetus.